Process for the production of trichlorocyanuric acid



Oct. 13, 1970 TQSHIHIRQ KAGAwA ETAL 3,534,033

PROCESS FOR THE PRODUCTION OF TRICHLOROCYANURIC ACID Filed June 15. 1968 2 Sheets-Sheet 1 F1 7 Quantity of NQIa m Llquid Reacmnt Fig.2

Quantityof Ncl3 irl Llqllld Reactant 10 'NC13 (g) Oct. 13, I970 TOSHIH IRO KAGAWA ETAL 3,534,033

PROCESS FOR THE PRODUCTION OF TRICHLOROCYANURIC ACID Filed June 13, 1968 2 Shets-Sheet 2 Fig 3 Qu mtity of NCIa in Llquid Reactant.

United States Patent 3,534,033 PROCESS FOR THE PRODUCTION OF TRICHLOROCYANURIC ACID Toshihiro Kagawa, 2018-2 Okadanishi, Ayauta-gun,

Kagawa-ken, Ayauta-machi, Japan, and Akira Ando,

1236 Shimmyo, Mitoyo-gun, Takase-machi, Japan Filed June 13, 1968, Ser. No. 736,769 Int. Cl. C07d 55/42 US. Cl. 260-248 6 Claims ABSTRACT OF THE DISCLOSURE A process for the production of trichlorocyanuric acid with safety and an excellent yield without forming nitro gen trichloride, the process comprising chlorinating cyanuric acid under specifically combined conditions of pH and temperature.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the production of the heterocyclic compounds and particularly of triazine derivatives.

Description of the prior art Cyanuric acid, of which the empirical formula being (CNOH) has in general the following structural formula:

Trichlorocyanuric acid has strong oxidizing power and is an extremely useful compound as a constituent of various commercial and domestic bleaching agents, disinfec-tants, and bactericides and as a general oxidant and chlorinating agent.

Heretofore, two processes for the chlorination of cyanuric acid have been well known: In one process, a mixture of cyanuric acid and an aqueous solution of an alkali metal compound as an alkaline agent is chlorinated below a certain pH value. In accordance with another process, chlorine is passed through a slurry of cyanuric acid kept at a constant pH value by adding an alkali to effect the chlorination, obtain a slurry of trichloro cyanuric acid, from which said trichlorocyanuric acid is separated by means of filtration, centrifugal separation, decantation, or the like. In these processes, however, in spite of the fact that safety was a major consideration, a large quantity of explosive nitrogen trichloride (which will be represented by NCl hereinafter) is formed.

NCl is an extremely unstable, yellow, oily liquid and is explosive upon impact, the action of an organic compound, or a temperature higher than 60 C. If NCl is accumulated in a plant, it is probable that a dangerous explosion will occur.

Due to the fact that the formation of NCl arises from the decomposition of trichlorocyanuric acid, in order to obtain trichlorocyanuric acid with excellent yield, it is necessary to inhibit the formation of NCl as far as is possible.

In order to remove NCI US. Pat. No. 2,970,998 discloses a process, in which NC1 contained in a slurry of trichlorocyanuric acid is after the chlorination, decomposed by means of bringing the slurry to pH 1.5 to 3.5 by adding thereto hydrochloric acid or sulfuric acid and maintaining the slurry in this state for 10 to 60 minutes. Alternatively, in accordance with the process of Japanese patent application publication No. 24,815 of 1964 filed on Aug. 6, 1962, NCl formed is removed from a slurry using an inert gas during or after the chlorination. However, in accordance with these processes, the yield of trichloro cyanuric acid is disadvantageously lowered, even if the NCI is removed.

It has heretofore been believed that the occurrence of the subsidiary reaction which accompanies the formation of dangerous NCl during the progress of reaction in the production of trichlorocyanuric acid is mainly due to the decomposition of the triazine ring of cyanuric acid which results from the chlorination thereof when the liquid reactant is in an alkaline state of higher than pH 9.0 during the earlier stage of the chlorination reaction as stated in the U3. Pat. No. 2,964,525 and Japanese Pat. No. 314,501. Accordingly, it has been preferred to produce trichlorocyanuric acid in such a manner that the pH value of the liquid reactant is adjusted so as to maintain it at lower than 9.0 and chlorine is reacted therewith until the final pH value is lower than 3.5, in order to carry the production into effect with safety and excellent yield. 7

However, it was found through experiments done by us and as described in the referential data hereinafter and illustrated in FIG. 1 that a great quantity of NCl is formed when the pH value of the liquid reactant is beween 7 and 5. Thus, whereas a little NCl 0.4 g. per mol of cyanuric acid, is formed in the pH value range for converting cyanuric acid into dichlorocyanuric acid, the range being higher than 8.0, a great quantity of NCl 9.2 g., is formed during the conversion of dichlorocyanuric acid to trichlorocyanuric acid, where the pH value is in the range of 5 to 7. In view of this, it was newly found that NCl is not formed by the chlorination of the triazine ring when the alkalinity is high as in the earlier stage of the chlorination, where the pH value is higher than 8.0, as disclosed in the above US. patent and the above Japanese patent, but rather, it is formed by the decomposition of the produced trichlorocyanuric acid, which occurs when same is attacked by an alkali when the pH value of the liquid reactant is in excess of 7.0 until it approaches 5.0. At the same time it was also found that it is possible to inhibit the formation of NCl by hastening the passage of the pH between 9 and 4 in the reduction of the alkalinity of the liquid reactant.

In accordance with the process described in Japanese Pat. No. 314,501, the reaction apparatus for the first stage is continuously charged with cyanuric acid, an alkali, and chlorine, the pH value being held therein at 5 to 9. The reaction mixture which is chlorinated therein is continuously partly removed therefrom and charged to another reaction apparatus, the pH value being held therein at 1.5 to 3.5, for further chlorination. Then trichlorocyanuric acid is continuously recovered from the second apparatus.

In accordance with process described in the US. Pat. No. 2,964,525, a solution of an alkali metal salt of cyanuric acid is charged to a reaction zone held at a pH lower than 4.5 for the continuous production of chlorocyanuric acid.

Through confirmation tests of these two processes it was found that the formation of NC];, is actually disadvantageously increased during the time the pH value is kept at 9 to 5 whereas it is stated in Japanese Pat. No. 314,501 that the reaction system is prevented from the formation by lowering the pH value down to lower than 9.0. In addition, the process of the last-named Japanese patent is not preferable since precipitations of dichlorocyanuric acid or a salt thereof are apt to separate out during the first stage of the reaction which is divided into two stages where the pH value is held at 9 to 5 whereby it becomes difficult to stir and transport the liquid reactant so that 3 the operation becomes troublesome. If the water content is increased in order to solve this problem, the formation of NCI and the loss of trichlorocyanuric acid due to resolution thereof increases, ending in a diminution of the yield.

Whereas it has been well known that the production of trichlorocyanuric acid by the chlorination of cyanuric acid is appreciably exothermic, and that the temperature of the liquid reactant must be kept rather low, removing the heat of reaction, for preventing the reactant from undergoing a subsidiary reaction due to the elevated temperature, the chlorination of the material of the liquid reactant having a pH value of 13.5 to 13.8 is done in haste until the pH value is reduced to lower than 4.5 in accordance with the process of the U.S. Pat. No. 2,964,525, which results in amplifying the calorific value. Therefore, there are such drawbacks that it is impossible to proceed with the reaction in excellent yield if the heat exchanging capacity is not particularly increased, resulting in problems in the provision of such a heat exchange, and also that there is difiiculty in excessive amplification of the chlorinating capacity. In addition, chlorine is not well absorbed due to the low pH value so that the utility rate of chlorine lowers.

What has been found by us through such tests for confirmation as above are that much NCl is formed in the prior art processes and that almost all of the NCl is formed during the time that the pH value is held at 7 to 4, in view of the fact that, while the formation of NCl is rather small during the periods where the pH value is 13.8 to 7 and lower than 4, much NCl is formed during the period when the pH value is 7 to 4.

It has been found that a small difference in the formation of NCI is derived from a difference between pH values to be maintained at such values as higher than 9 and lower than 4 and that it is possible to reduce the formation of NCl if the process is made to rapidly pass through the range of 9 to 4 in pH value where much more NCl is formed. In short, a remarkably small quantity of NCl is formed at a pH value of higher than 9 and lower than 4 in the liquid reactant and much is formed between pH 9 and 4.

Thus it has been found by us that a smaller quantity of NCl is formed by dividing the reaction into two stages, where such ranges of pH value of the liquid reactant where small quantities of NCl are formed there, respectively, are combined, and making the process pass instantaneously through the range of 9 to 4 in pH value of the liquid reactant, than in any other processes, whereby it is possible to eliminate the overall drawbacks as described hereinbefore. This invention is based on such studies as above.

These studies will now be specifically referred to in the following referential data, which may be considered in connection with the drawings.

REFERENTIAL DATUM In this referential datum, resulting from tests, the quantity and period of the formation of NCl were studied in the case where trichlorocyanuric acid was produced in accordance with the well known prior art.

A titanium reaction vessel having a capacity of three liters, and equipped with a mechanical stirrer, a charge inlet, a chlorine inlet, a gas outlet, an overflow pipe for removing formed slurry, a lower outlet, a thermometer, and a pH meter was provided. In order to adjust the temperature of the liquid reactant, the reaction vessel was immersed in ice water during the chlorination.

1.5 liters of water, 3 mols of caustic soda, and 1 mol of cyanuric acid were put in the reaction vessel and stirred so as to be dissolved, thereby obtaining a trisodium cyanurate solution. At an adjusted temperature of 10 to C., gaseous chlorine was charged thereto at a rate of 1 liter per minute. The pH value of the solution was successively lowered in accordance with the introduction of 4 chlorine starting from 13.8 in pH value and finally the pH 2.0 when the introduction was completed. The liquid reactant was sampled in accordance with the change in pH value for measuring NCl formed. After the reaction, trichlorocyanuric acid produced was filtered, washed with water, and dried. The dried product was weighed for the yield and the effective chlorine. The efiective chlorine of the produced trichlorocyanuric acid thus estimated was 90.35 and the product, corrected for the removed sample was g., so that the yield was accordingly 73.3%.

The formation of NCl was estimated quantitatively as follows: The gaseous output was introduced into concentrated hydrochloric acid contained in an absorbing bottle so as to convert same to ammonium chloride for the purpose of estimation. In addition, NCl formed and kept in the liquid reactant was dissolved into carbon tetrachloride by stirring same together with the sample of the liquid reactant. The carbon tetrachloride was treated with concentrated hydrochloric acid so as to convert the NCl into ammonium chloride for the purpose of estimation. The results are tabulated as follows:

TABLE 1 Quantities of NCl accumulated in the liquid reactant at various pH values successively changed pH values of liquid reactant: NCl therein g. 0

TABLE 2 Differences in quantities of NCl between two adjacent pH values in Table 1 NCl formed pH values of liquid reactant changed: in the period g.

FIG. 1 of the appended drawings is a graph representing the interrelation of the quantities of NCI formed and accumulated in the liquid reactant at various pH values successively changed with the variation in pH value corresponding to Table 1.

From the studies shown in this referential datum 1, it was found that the formation of NCl increases suddenly when the pH value of the liquid reactant is lowered down to lower than 7 in the later half of the chlorination reaction. In view of the fact that the quantity of chlorine supplied to the liquid reactant before the pH value arrives at 7 in the liquid reactant corresponds to two-thirds of the total quantity of chlorine required for completing the reaction, it is supposed that the time is such that the whole quantity of cyanuric-acid used is just converted into sodium dichlorocyanurate and that the formation of NCl increases suddenly when the dichlorocyanurate is case where dichlorocyanuric acid isproduced in accordance with the generally well known prior art, it is possible to operate with safety, reducing the formation of NC1 REFERENTIAL DATUM 2 By this referential test it was found that, even in the 1.5 liters of water, 2 mols of caustic soda, and 1 mol of cyanuric acid were placed in the reaction vessel as used in the preceding test, thereby obtaining a solution. Gaseous chlorine was charged thereto at a rate of 1 liter per minute at an adjusted temperature of 10 to C. The pH value of the liquid reactant was lowered successively corresponding to the introduction of chlorine starting from pH 13.2. The introduction of chlorine was stopped when the pH value arrived at 3. The yield of dichlorocyanuric acid was treated as in the preceding test. Thus 71.5% of chlorine had been assigned to the resulting dichlorocyanuric acid as the effective chlorine. The yield was 178.9 g., so that the yield based on cyanuric acid was 90.3%, while the formation of NCl was 0.748 g. Thus it was found that, even when dichlorocyanuric acid is produced in accordance with the well known prior art as it is, the operation may be carried out with safety, forming a little quantity of NCl 3O REFERENTIAL DATUM 3 'This referential test relates to the case where trisodium cyanurate was used for chlorinating the same while maintaining the pH value of the liquid reactant at a constant value.

A trisodium cyanurate solution was prepared by dis solving 15 mols of caustic soda and 5 mols of cyanuric acid into 9.7 liters of water. Using the reaction vessel referred to in the preceding data, 0.5 liter of water was adjusted in temperature to 10 to 15 C. and in pH value to a constant value by adding chlorine to the above trisodium cyanurate solution. Thereafter, while gaseous chlorine was introduced thereto at a rate of 1 liter per minute, chlorination was carried out in such a manner that a constant pH value was maintained by adding thereto the above trisodium cyanurate solution continuously. The chlorinated liquid reactant was taken out of the vessel continuously through the overflow pipes. The quantity of NCl was measured as in the referential datum l.

Similar tests were effected with respect to various pH values. The following tables illustrate the pH values maintained, the formation of N Cl per 1 mol of cyanuric acid, and chlorine absorbed.

Two pH values compared: Difference in formation of N01 FIG. 2 is a graph representing the interrelation of the quantities of NCl formed at the liquid reactant maintamed in various pH values therewith and corresponds to the second line of Table 3.

From the above studies, it was found that, although much NCl is formed in the casethe pH value is maintained at 5, 6, or 7, it is not deemed that, even if the pH 7 value is maintained at a lower value than 9, the formation NCl becomes small. It is also found that the absorption of chlorine is poor when the pH value is maintained lower than 5. The difference in the formation of NCl between two pH values having the difference of 1 unit is small when the pH value maintained is higher than 9 and lower than 4 while it is large between 5 and 9. Thus it was found that, if the reaction is made to pass instantaneously through the range of pH values which is apt to form N01 it is possible to minimize the formation of NCl REF ERENTIAL DATUM 4 From this referential test it was found that it is possible to operate with safety with a more reduced formation of NCl than in any process of producing trichlorocyanuric acid when the chlorination'reaction is divided into two stages, the pH value of the liquid reactant being maintained higher than 9 during the first stage and at 3 during the second stage for the chlorination.

15 mols of caustic soda and 5 mols of cyanuric acid Were dissolved in 9.7 liters of water thereby obtaining a trisodium cyanurate solution. Two reaction vessels as referred to in the preceding tests were charged with 0.5 liter portions of water and adjusted to a temperature to 10 to 15 C. The pH value of the water contained in the first reaction vessel was adjusted at a certain value, the variation of which was tested in a series of runs, and the pH in the second reaction vessel was at 3, by adding chlorine or the trisodium cyanurate solution. Then the first vessel'was charged with the trisodium cyanurate solution continuously at a constant rate, from whence, after chlorination, the. chlorinated liquid reactant was partly overflowed continuously into the second reaction vessel where the liquid reactant was further chlorinated into a slurry of trichlorocyanuric acid which was partly overflowed continuously for removing same from the second vessel.

Chlorine was fed in such a manner that the pH value of 3 was maintained in the second reaction vessel and the Differences in quantities. of NCl between two tests in which pH values werev maintained constant with a difference of 1.

Two pH values compared: Difference in formation of N01 13, 12 0.02 l2, 11 0.03 11, 10 0.10 10, 9 V 0.11 9, 8 0.40

TABLE 3 NCla formed and chlorine absorbed in the liquid reactant of which pH was maintained constant at various values, respectively pH value of the liquid reactant maintained-.. is 12 11 10 9 s 7 s 5 4 a 2 NC]; in the reactant,g 0.04 0.06 0.09- 0.19 0. 0.70 1. 05 4.30 9. '10 2.3 2.6 2. 55 Absorption of 01, percent 100 100 100 100 100 99.0 97.1 92.4 85,8 78.2 68.3

TABLE 4 predetermined value to be tested was maintained in the 65 first reaction vessel into which unabsorbed chlorine in the second vessel was fed together with fresh chlorine. The whole quantity of the trisodium cyanurate solution was treated as above, thereafter the chlorinated product was treated similarly as in the referential test 1.

In the series of this test, the pH, value in the second re action vessel was maintained at a constant value of 3 while in the first reaction vessel each of the nine variations, from 4 to 12, in the pH value was maintained for testing. The results were converted into data based on 1' mol of cyanuric acid and tabulated as follows:

TABLE Interrelation of pH at which the first stage reaction vessel was maintained, to the quantity of NC]; formed in the liquid reactant and the yield of product pH in 1st stage 4 5 s 7 s 9 11 12 N01 in reactant, g 2. 7 9. 8 5. l 3. 5 3. 2 1. 9 1. 3 1. 2 1. 1 Yield of product: Grams 109. 4 186. 7 191. 6 196. 0 196. 9 202. 5 204. 6 208. 8 207. 6

Percent 85. 8 80. 3 82. 5 84. 3 84. 7 87.2 88. 1 89.8 89. 3

Norm-A constant pH value of 3 was maintained in the second stage reaction vessel throughout the series or the referential test 4.

FIG. 3 is a graph representing the interrelation of the pH value at which the first stage reaction vessel was maintained, to the quantity of NCl formed, corresponding to to the second line of Table 5.

From this referential test, it was found that, by dividing the chlorination reaction into two stages, the pH of the liquid reactant during the first stage reaction being maintained at higher than 9 and that during the second stage reaction at 3, trichlorocyanuric acid is produced with the formation of a small quantity of NCl and in excellent yield.

REFERENTIAL DATUM 5 This referential test is such that, by virtue thereof it was found that the formation of NCl may be reduced by reducing the quantity of water for preparing the aqueous solution of trisodium cyanurate.

A series of tests were effected similarly to the preceding referential test. The second reaction vessel was maintained at pH 3 while the first stage reaction vessel was at pH 6 and the test was repeated also for pH 8, 10, and 12 in place of the pH of 6 of the first stage reaction vessel. As to each of these four cases, the quantity of water for preparing the aqueous solution of trisodium cyanurate was varied from 7.5 times to units of water per unit quantity of cyanuric acid. The following are the tabulated results from these series of tests.

TABLE 6 Interrelation of quantity of water used to the formation of N61 pH in reaction vessel of 1st Stage Times 6 8 10 12 Quantity of water per 7. 5 0.91 0.83 unit quantity of eyanuric 1. 03 0. 91 acid. 12. 1. 17 1. 00 1. 1. 10 17. 5 5. 3. 34 1. 43 1. 24 20. 0 5. 60 3. 53 1. 59 1. 37

TABLE 7 Inter-relation of the quantity of water used to the yield pH in reaction vessel of 1st stage Times 6 8 10 12 Quantity of water per 91. 3 92. 7 unit quantity oi eyanuric 90. 8 92. 0 acid. 12. 89. 4 90. 6 15. 0 82. 5 84. 7 88. 1 89. 3

SUMMARY OF THE INVENTION This invention has been completed on the basis of the facts clarified as results of the above referential tests and many other repeated experiments.

The process of producing trichlorocyanuric acid in accordance with this invention comprises chlorinating cyanuric acid in an aqueous medium by the steps of (1) adding to the cyanuric acid a hydroxide of a metal as an alkaline agent which is necessary for the production of trichlorocyanuric acid, (2) dividing the chlorination reaction into two stages, the pH value being maintained in the liquid reactant at above 9 during the first stage and at below 4 during the second stage, (3) the temperature of the liquid reactant being maintained between the freezing point of said liquid reactant and 40 C., (4) the chlorination being effected batchwise or continuously for the first stage reaction and continuously for the second stage reaction, (5) the chlorination being completed by letting the liquid reactant through a reaction vessel for the first stage reaction and another reaction vessel for the second stage reaction, and (6) separating the precipitate out of the reaction mixture formed.

By virtue of this process, not only is it possible to carry out the operation extremely safely and simply, but the danger of explosion is eliminated by inhibiting the formation of dangerous NCl and also the yield of trichlorocyanuric acid produced may be increased up to the extent of which may be compared with about 75% achieved by the process in accordance with the well known prior art, so that the present process is extremely advantageous from the commercial standpoint.

BRIEF DESCRIPTION OF THE DRAWING The studies in connection with the prior art described hereinabove for comparing same with this invention will be better understood by those skilled in the art upon reference to the following drawings, in which:

FIG. 1 is a graph representing the interrelation of the quantity of NCl in the liquid reactant at various pH values which are successively changed;

FIG. 2 is a graph representing the interrelation of the quantity of NCl in the liquid reactant at various pH values therewith, as to which some tests were similarly effected; and

FIG. 3 is a graph representing the interrelation of the quantity of NC];; in the liquid reactant at various pH values which are successively changed through a series of tests of the operation of the first stage of the reaction divided into two stages.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1.-In this example trichlorocyanuric acid was produced by the process in which the alkaline agent was caustic soda, the pH in the reaction vessel for the first stage reaction was maintained at 9.5, and that in the reaction vessel for the second stage reaction was maintained at 4.

An aqueous solution of trisodium cyanurate was prepared by dissolving 15 mols of caustic soda and 5 mols of cyanuric acid in 9.7 liters of water. Two reaction vessels described in the referential datum 1 were used for the first stage reaction and the second stage reaction, respectively. Each vessel was fed with 0.5 liter of water and adjusted to a temperature of 10 to 15 C. The water contained in the first stage reaction vessel was adjusted to pH 9.5 and that in the second stage reaction vessel was to 4 in pH value by admitting a quantity of the trisodium cyanurate solution and gaseous chlorine thereto. The trisodium cyanurate solution was then entirely and continuously charged into the first stage reaction vessel. Gaseous chlorine was also admitted thereinto in the manner described below. The chlorinated liquid reactant was partly overflowed into the second stage reaction vessel whereby a slurry of trichlorocyanuric acid was continuously formed. Gaseous chlorine was supplied into the second stage reaction vessel in such a manner that the pH value in the vessel was maintained at 4. Unabsorbed gaseous chlorine in the second stage reaction vessel was removed therefrom and supplied to the first stage reaction vessel together with a quantity of fresh gaseous chlorine as mentioned above. Such gaseous chlorine was admitted into the first stage reaction vessel in such a manner that the pH value in the first stage reaction vessel was maintained at 9.5. The slurry in the second stage reaction vessel was partly overflowed therefrom for taking same out thereof continuously. Trichlorocyanuric acid and NCl produced thereby were treated as in the referential test 1.

NCl formed weighed 1.42 g. by converting into the value per mol of cyanuric acid. 203.9 g. of trichlorocyanuric acid were produced, having an effective chlorine of 90.6%. Accordingly, the yield was 87.7%.

Example 2.-In this example trichlorocyanuric acid was produced under conditions such that the first stage reaction vessel was maintained at pH 11 and the second stage reaction vessel was maintained at pH 3.

An aqueous solution of trisodium cyanurate was prepared by dissolving 15 mols of caustic soda and mols of cyanuric acid into 6.5 liters of water. Two reaction vessels similar to those used in the preceding example were used. The pH values in the two vessels were adjusted to 11 and 3, respectively, and maintained thereat throughout the operation. Trichlorocyanuric acid was thus produced and treated similarly as in the preceding example.

The results converted into the values per mol of cyanuric acid were as follows: The formation of N01 was 0.98 g. The production of trichlorocyanuric acid was 212.5 g. of which the elfective chlorine was 90.3%. Accordingly, the yield was 91.3%.

Example 3.-In this example trichlorocyanuric acid was produced similarly to Example 2 but using caustic potash as the alkaline agent.

An aqueous solution of tripotassium cyanurate was prepared by dissolving 15 mols of caustic potash and 5 mols of cyanuric acid into 6.5 liters of water. The chlorination reaction was carried into effect under similar condition to the Example 2. Results converted into the values per mol of cyanuric acid were as follows: The formation of NCl was 1.01 g. The production of trichlorocyanuric acid was 212.1 g. of which the effective chlorine was 90.4%. Accordingly, the yield was 91.2%.

Example 4.-In this example trichlorocyanuric acid was produced under conditions such that the first stage reaction was operated batchwise while maintaining the pH value above 9 and the second reaction was operated continuously maintaining the pH value lower than 4.

An aqueous solution of trisodium cyanurate was prepared by dissolving 15 mols of caustic soda and 5 mols of cyanuric acid into 8 liters of water.

2 liters of the solution were placed in the first stage reaction vessel as referred to in the preceding examples and 0.5 liter of water was placed in the second stage reaction vessel as referred to in the preceding examples. The temperatures of these vessels were adjusted to 10 to C., respectively. The pH values for the first stage and for the second stage were adjusted respectively to 12 and 3 by chlorine addition. The first stage reaction was carried out on the solution supplied batchwise while the liquid reactant formed was taken therefrom continuously and supplied to the second stage reaction vessel where a slurry of trichlorocyanuric acid was produced. Produced slurry was partly continuously overflowed therefrom. Because of such manner of the operation, the pH value maintained at 12 in the first stage reaction vessel at first dropped to 9 due to the progress of chlorination and the reduction of the quantity of the liquid reactant. When the pH value was lowered to 9, a fresh solution of trisodium cyanurate was supplemented to the first reaction vessel so that the pH value was restored to 12: thus the value was varied between 12 and 9 repeatedly. Meanwhile, the pH value in the second stage reaction vessel was maintained lower than 4 by means of adjusting the supply of chlorine. Unabsorbed chlorine in the second stage reaction vessel was directed to the first stage reaction vessel together with fresh chlorine. Trichlorocyanuric acid and NC1 produced were treated as in the preceding example.

Being converted into values per mol of cyanuric acid, 1.16 g. of NCI was formed and 208 g. of trichlorocyanuric acid were produced, which has 89.8% of effective chlorine. Accordingly, the yield was 89.4%

Example 5.In this example the first stage reaction was carried out so as to lower the pH value to 10. The liquid reactant obtained by the first stage reaction was further chlorinated continuously, the pH value being maintained at 3.5, to produce trichlorocyanuric acid.

2 liters of a solution of trisodium cyanurate as described in Example 4 were placed in a vessel as described in the preceding examples. The temperature of the solution was adjusted to 10 to 15 C. Gaseous chlorine was admitted into the solution at a rate of 2 liters per minute so as to lower the pH value. When the pH value had been lowered to 10, the liquid reactant was removed from the vessel. Repeating as above, the entire solution was chlorinated to the liquid reactant having the pH value of 10. The empty reaction vessel was charged with 0.5 liter of water, of which the pH value was adjusted to 3.5. Gaseous chlorine and the liquid reactant were continuously supplied to the water, the supply of the former being at a rate of 1 liter per minute, in such a manner that the pH value of the liquid reactant was maintained at 3.5, so as to further chlorinate the liquid reactant, yielding a slurry of trichlorocyanuric acid. Taking out the slurry of the vessel, a product was obtained by treating it similarly to the preceding example.

Being converted into values per mole of cyanuric acid, 1.13 g. of NCl was formed and 209.2 g. of trichlorocyanuric acid were produced, which has 90.5% of effective chlorine. Accordingly, the yield was 89.9%.

Example 6.In this example a slurry of cyanuric acid and a solution of caustic soda were substituted for the trisodium cyanurate.

A slurry prepared by adding 5 mols of cyanuric acid to 4.7 liters of water and a solution prepared by dissolving 15 mols of caustic soda in 5 liters of water were provided.

The chlorination reaction was carried into eifect similarly to Example 1 but the above slurry and the solution were substituted for the trisodium cyanurate, in which the proportion was 1 mol of the cyanuric acid slurry to 3 mols of the caustic soda solution. All other conditions were similar to that of Example 1.

Being converted into the values per mol of cyanuric acid, 1.34 g. of NC1 was formed and 205 g. of trichlorocyanuric acid were produced, of which the eflt'ective chlorine was 90.1%. Accordingly the yield was 88.2%.

Example 7.-In order to satisfy a specific request, trichlorocyanuric acid having less effective chlorine was produced. To this end, a smaller quantity of caustic soda was;i used in proportion to the quantity of cyanuric acid use A slurry prepared by adding 5 mols of cyanuric acid to 4.7 liters of water and a solution prepared by dissolving 14 mols of caustic soda to 5 liters of water were provided.

The chlorination reaction was carried into effect using the slurry and the solution, instead of the trisodium cyanurate in Example 1. The first stage reaction vessel was charged with the slurry and the solution continuously at a rate of 2.8 mols of caustic soda per mol of cyanuric acid. Other conditions were similar to those in Example 1.

Being converted into values per mol of cyanuric acid, the results are the formation of 0.94 g. of NCl and the production of 201 g. of trichlorocyanuric acid having 86.5% of effective chlorine. Accordingly the yield was 86.5

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A process for the production of trichlorocyanuric acid by chlorinating cyanuric acid in an aqueous medium, comprising the steps of preparing a slurry or a solution containing cyanuric acid and caustic alkali, charging a first stage chlorinating reaction zone with said slurry or said solution together with gaseous chlorine intermittently or continuously under conditions such that the pH value of the liquid reactant is always maintained at a value higher than 9 and that the temperature thereof is always maintained at a temperature bet-ween the freezing point of said liquid reactant and 40 C., to react said liquid reactant with the chlorine, removing the resulting liquid reactant partly and continuously from said zone, continuously charging a second stage chlorinating reaction zone with said removed liquid reactant together with additional gaseous chlorine under conditions such that the pH value of the last-named liquid reactant is always maintained at a value lower than 4 and that the temperature thereof is always maintained at a temperature between the freezing point thereof and 40 C., to react the last-named liquid reactant with the last-named chlorine, removing the resulting liquid reactant partly and continuously from the last-named zone, and separating crystals of trichlorocyanuric acid precipitated from the lastnamed removed liquid reactant.

2. A process as defined in claim 1, in which said caustic alkali is a member selected from the group consisting of caustic soda and caustic potash.

3. A process as defined in claim 1, in which said caustic alkali is a mixture of caustic soda and caustic potash.

4. A process as defined in claim 1, in which said charging of the first stage chlorinating reaction zone with a slurry or a solution, containing cyanuric acid and caustic alkali, is effected with a slurry or a solution of an alkali metal cyanurate.

5. A process as defined in claim 1, in *which said first stage chlorinating reaction zone is charged with separate portions of said cyanuric acid and said caustic alkali.

6. A process as defined in claim 1, in 'which the molar quantity of said caustic alkali to be charged is from 2.5 to 3.2 times the quantity of said cyanuric acid.

References Cited UNITED STATES PATENTS 4/1965 Vazopolos 260248 5/1965 Frazier 260-248 

